The simplest known mechanisms for protecting trailers against theft are locks on the king pin, thus, making it mechanically impossible to couple the trailer. However, they are inconvenient and expensive, and must be unlocked by mechanical action.
Vehicle brake systems that provide anti-theft protection are also known, which provide a valve in a pressurized-fluid line that depressurizes the fluid-pressure line in order to engage the brake. Such known systems combine the function of the valve with the actuation of a key, for example, so that the parking brake is released only if a key has been appropriately employed. A disadvantage of such systems is that the parking brake can be enabled only if the right key is in the possession of the person who wishes to remove the trailer. In addition, this conventional approach does not offer any flexible protection capable of being adapted to complex logistics.
To improve the reliability of the above anti-theft safeguard, the valve device can be interlocked by means of a coded electronic package integrated into the brake system so that not only the supply voltage but also an additional enabling operation is needed to unlock the valve device. Although these known anti-theft safeguards already have many advantages and, in particular, a heightened degree of security and reliability, it can be a disadvantage that current must be continuously present at a valve device in order to release the parking brake. If the valve device is isolated from the voltage supply, the valve immediately reverts to a condition in which the parking brake system is again engaged. A hazard might be presented in situations in which a trailer having such a brake system is inadvertently decoupled from the tractor, thus interrupting the voltage supply. To this extent, the operator control capability of these conventional protective devices is restricted to the functions offered by the integrated electronics package. Greater flexibility and adaptability of the protective mechanisms is not known.